Without limiting the scope of the invention, its background is described in connection with integrated circuits including a plurality of different semiconductor devices, for example.
Heretofore, normal diffused source/drain metal oxide semiconductor (DMOS) transistors were built using diffused channel regions and diffused source/drain regions. After the growth of a gate insulator on the surface of a semiconductor substrate or epitaxial layer, a doped polysilicon gate was deposited, doped, patterned and etched. The gate, either by itself or as augmented with sidewall oxide regions, was used to register the self-alignment of a (p) type implant (where the semiconductor region in which the device was to be formed, was of (n) type).
Prior to this time, channel stop implants and any threshold voltage adjust implant was done into the face of the semiconductor layer. The (p) type implant then was subjected to a long diffusion cycle, such as for 1100.degree. C. for approximately 500 minutes. This diffusion is followed by the self-aligned implant of (n) type source/drain regions.
When lateral and vertical DMOS transistors are built within an integrated process, however, problems arise because of the non-uniform rate of diffusion of the (n) type source/drain regions and the (p) type channel region previously implanted. The channel region, which is supposed to diffuse underneath the poly gate to a greater extent than the source/drain regions, will often find itself with unacceptedly reduced metallurgical channel lengths, or channel lengths which are otherwise insufficiently controlled.
In recent years, as integrated circuits have become more and more prevalent as connected to automotive electrical systems and the like, it has become desirable to build integrated circuits which are compatible with these often poorly regulated electrical systems. A typical automobile electrical system can, for example, experience transients as high as 60 volts.
On the other hand, the countervailing object of semiconductor device size reduction mandates that the semiconductor devices on an integrated circuit chip meant for automotive use operate using small voltages and currents. Devices such as 5-volt n-channel field effect logic transistors, for example, would fail if exposed to the high voltages, transients and current densities that an automobile electrical power system is liable to provide. It has therefore become desirable to design transistor and other semiconductor components that have additional protection against such high voltage transients.
Accordingly, improvements which overcome any or all of the above noted problems are presently desirable.